1. Field of the Invention
This invention relates to a circuit arrangement for igniting at least one gas discharge flash tube which has two main electrodes connected to a voltage generator that supplies an ignition voltage pulse and parallel to a chargeable flash capacitor and an electronic switch.
2. Description of the Prior Art
Gas discharge flash lamps (flash tubes) serve for producing short intensive light flashes. Heretofore, the electrical energy stored in a capacitor (a flash capacitor) is converted into light through the ignition of a gas discharge in a high current arc operation. The ignition is effected by way of a high voltage pulse with which the discharge path is charged, in particular usually by way of an ignition electrode which is provided on the exterior of the flash tube, and usually in the form of a conductor in addition to the main electrodes. Since, however, an ignition electrode requires a technical expense and safety problems, i.e. the danger of touching by an operator, it has been considered that to an increasing extent to directly apply a high voltage pulse for causing an ignition of the gas discharge directly to the two main electrodes of the flash tube.
In order to ignite gas discharge flash lamps without utilizing an ignition electrode, the flash tube, the flash capacitor and the ignition voltage pulse generator may be quickly switched one behind the other. Then, the discharge current which produces the flash of light will flow by way of the ignition voltage pulse generator. Generally, the ignition voltage pulse generator is a transformer which has a secondary winding connected in the discharge circuit, which winding must not only stand the stress of the discharge current but also, due to its inductivity, must change the discharge operation in an undesired manner.
The aforementioned difficulties can be avoided when the secondary winding of the ignition transformer is connected in parallel to the flash tube. Such a circuit can be seen by reference to the German Offlegungschrift 1,638,977, for example. In that reference, a short circuiting of the ignition voltage pulse by way of the flash capacitor is prevented with the help of one or more diodes connected in the discharge circuit. Even if such a circuit has the advantage that the duration of the discharge process, thus the flash duration, is essentially only determined by the internal resistance of the flash tube and the capacitance of the flash capacitor, there still remains the drawback that only one-half wave of the ignition voltage pulse can become effective at the flash tube. Furthermore, the demands on the electronic properties of the diodes which are connected in the discharge circuit in series with the flash capacitor, are very high, since these diodes must be designed for high voltages in the blocked direction and high currents in the pass direction.